DESCRIPTION: (Applicant's Abstract) The main goal of this proposal is to study the cellular mechanism of the early inhibitory effect of glucocorticoids on Dynorphin-stimulated ACTH release. To accomplish this goal, three specific aims were established: (1) to determine if glucocorticoids inhibit Dynorphin-stimulated ACTH release acting directly on corticotrophs of anterior pituitary. This will be accomplished by determing the effects of dexamethasone on Dynorphin-stimulated ACTH secretion from mouse anterior pituitary tumor cells. (2) to test if glucocorticoid inhibitory action is mediated via glucocorticoid type II receptors and activation of guanylyl cyclase. Glucocorticoid type II receptor antagonists RU28362 and RU26988 will be used to study their effect on dexamethasone inhibitory action. To test the role of cGMP, dexamethasone-stimulated cGMP formation will be determined, followed by the use of the guanylyl cyclase inhibitor LY83583 and Br-8-cGMP to see the importance of cGMP in inhibition Dynorphin-stimulated ACTH release. (3) to study a role of voltage-dependent calcium channels and calcium-dependent potassium channels in glucocorticoids inhibitory action on Dynorphin-stimulated ACTH release. Whole cell perforated patch-clamp will be used to study any changes in dexamethasone stimulated calcium and potassium currents. In addition, specific inhibitors of voltage-dependent calcium currents and calcium-dependent potassium currents will be used to study their effects on dexamethasone inhibition of Dynorphin-stimulated ACTH release. An understanding of the regulatory control Dynorphin-stimulated ACTH secretion is important, because Dynorphin has been shown to inhibit the development of tolerance to opioids to eliminated the development of sensitization to cocaine, thus making it a good drug for treatment of drug abuse.